We owned two chihuahua-Tenterfield terrier cross dogs, a brother and sister when we lived in the Northern Tablelands of New South Wales, where the winters are very cold.
They both loved to snooze in the winter sun out of the wind, so my husband made them a weatherproof box with most of the opening covered with perspex. We placed it so it faced north.
Whichever dog ran in first would claim the shelter and not allow the other one to enter. The female worked out that if she wanted to get in, she only had to go to the yard gate and let out an alarmed bark. This would prompt her brother to leave the box alone in order to investigate – allowing her to hurry inside. This happened many times over the years and he fell for it every time.